Progress in LED Technology
Despite its extensive use for more than 40 years the light-emitting diode (LED) remains a mystery to its millions of users – the majority of whom have long taken for granted these small light sources that seem to exist in almost every electronic device, from clock radios to traffic lights

Even those sufficiently informed to realise that an LED is a solid-state semiconductor device that emits light when an electric current passes through it probably only know a few of the attributes that contribute to one of most remarkable growth patterns the lighting world has ever known. Following the development of a new generation of materials, particularly over the last decade, and quite apart from continued improvements in brightness, life, colour quality and the range of shapes and sizes, the efficacy of current bareLEDs for general lighting are now above 100 Lm/W compared to the limited red indicator of the late 1960s, however after the addition of optics and the embodiment in a luminaire this is significantly reduced and could be less than half this in practice, and its useful life has been extended to around 50,000 hours. In short, it is now considered a mainstream lighting technology.